1. Field of the Invention
This invention relates to injectors of the type used to meter fuel in internal combustion engines. Particularly in autoignition engines equipped with high-pressure accumulators, the nozzle needle is hydraulically triggered to open and close the injection openings. The hydraulic pressure in the control chamber required for this is generated by means of boosters triggered by actuators.
2. Prior Art
In fuel injectors of the type used in the prior art, an actuator triggers a control valve. For example, the actuator is embodied in the form of a piezoelectric actuator or an electromagnetic actuator. The control valve opens or closes a connection from a pressurized control chamber into a low-pressure line. One side of the control chamber is delimited by an end surface of the nozzle needle that opens or closes the least one injection nozzle. Once the control valve has opened, the pressure in the control chamber drops. This simultaneously decreases the compressive force acting on the nozzle needle. Once the force oriented in the opposite direction exceeds the compressive force acting on the end surface of the nozzle needle delimiting the control chamber, then the nozzle needle moves into the control chamber, thus unblocking the at least one injection opening. In order to close the injection opening, the control valve is closed again, causing the pressure in the control chamber to increase again. Once the compressive force acting on the end surface of the nozzle needle, which increases due to the rising pressure, exceeds the forces acting on the nozzle needle in the opposite direction, then the nozzle needle moves toward the injection opening and closes it.
If a piezoelectric actuator is used as the actuator, then this design of the fuel injector means that the piezoelectric actuator is supplied with current and thus experiences a longitudinal expansion when the injection nozzles are closed. To open the injection nozzles, the voltage is simply disconnected from piezoelectric actuator. The actuator is therefore continuously supplied with current in the closed state.
Another disadvantage of the fuel injectors known from the prior art is that the high boosting ratio from the actuator to the nozzle needle of 1:4 reduces the rigidity of the injector system, particularly in the lower partial stroke, thus making it impossible to adequately shape the injection curve.